Download Measuring Earthquakes Volcanoes

Section 2: Earthquakes and Volcanoes
Preview

Key Ideas

Bellringer

What are Earthquakes?

Measuring Earthquakes

Volcanoes
Key Ideas
Where do most earthquakes occur?
How do scientists learn about
earthquakes and the Earth’s interior?
What is a volcano?
Bellringer
Imagine a corked bottle of soda pop that is
standing in a pan of hot water.
1. What do you think will happen as the soda pop
heats up?
2. What happens when the pressure builds up in
the soda pop?
3. Molten rock in Earth’s mantle is like the soda pop.
What happens when pressure builds up in Earth’s
mantle?
What are Earthquakes?
Earthquakes are vibrations resulting
from rocks sliding past each other at a
fault.
〉 Where
do most earthquakes occur?
- mostly at the boundaries of tectonic
plates
What are Earthquakes?
continued
 Seismic
waves are waves of energy
released during an earthquake.
Focus: the location within Earth along a fault at
which the first motion of an earthquake occurs
Epicenter: the point on Earth’s surface directly
above an earthquake’s starting point, or focus
Focus and Epicenter
What are Earthquakes?

continued
Energy is transferred by waves.
 The
energy released from an earthquake is
measured as shock waves.
3
types of waves:
Longitudinal
waves, also known as P
waves
Transverse
Surface
waves, also known as S waves
waves
What are Earthquakes?
continued
Longitudinal waves
-
travel by compressing and stretching crust.
-
(P waves).
Transverse waves
- travel in an up and downward movement.
(S waves).
Visual Concept: Longitudinal Waves
Visual Concept: Transverse Wave
What are Earthquakes?
continued
 Both
P waves and S waves spread out from the focus
in all directions through the earth.
 Surface waves move only on Earth’s surface.

surface wave: a seismic wave that travels along
the surface of a medium

-has a stronger effect near the surface of the
medium than it has in the interior
Visual Concept: Seismic Waves: Surface Waves
Measuring Earthquakes
〉
How do scientists learn about earthquakes and the Earth’s interior?
〉Because
energy from earthquakes is
transferred by waves, scientists can
measure the waves to learn about
earthquakes and about the interior
of Earth through which the waves
travel.
Measuring Earthquakes,

continued
Seismologists detect and measure earthquakes.



Three seismograph stations are necessary to
locate the epicenter of an earthquake.
Geologists use seismographs to investigate
Earth’s interior.
The Richter scale is used to measure
earthquakes.
Visual Concept: Seismographs and Mapping Earth’s
Layers
Measuring Earthquakes,


continued
There are more than 1000 seismograph stations across the world.
Because P waves travel faster, the difference between the arrival of P waves
and the arrival of S waves allows scientists to calculate how far away the focus
is.
The way P and S waves travel through Earth’s interior helps scientists make a
model of Earth with layers of different densities.
 Scientists have used this information to develop a model of Earth’s interior
structure.

Richter scale: a scale that expresses the magnitude
of earthquakes
Volcanoes
〉
A volcano is any opening in Earth’s crust through which
magma has reached Earth’s surface.
Visual Concept: Magma and Vents
Volcanoes
 Shield
volcanoes have mild eruptions.
 are
some of the largest volcanoes due to
gently sloping sides (not tallest).
 Composite
volcanoes have trapped gas.
 made
of alternating layers of ash, cinders,
and lava.
 usually very steep due to alternating layers
 Cinder
cones are the most abundant
volcanoes.
 are
the smallest because the steep sides
erode quickly.
Volcanoes
Visual Concept:
Types of Volcanoes
Volcanoes, continued

Most volcanoes occur at convergent plate
boundaries.
 75%
of the active volcanoes on Earth are located in
an area known as the Ring of Fire.
 The Ring of Fire is located along the edges of the
Pacific ocean, where oceanic tectonic plates are
colliding with continental plates.
Volcanoes, continued
 Underwater
volcanoes occur at
divergent plate boundaries.
At
divergent boundaries, magma rises
to fill the gap.
 volcanic mountains here will form
ocean ridges.
Iceland is a volcanic island on the MidAtlantic ridge that is growing outward
in opposite directions.
Visual Concept: Hot Spots and Mantle Plumes
Volcanoes,

continued
Volcanoes can occur at hotspots.
 Some
volcanoes occur in the middle of plates.
 Mantle
plumes -mushroom shaped trails of hot
rock from deep inside the mantle. Melt as they
rise, and erupt from volcanoes at hot spots.
 The
plumes remain in the same place as the
tectonic plate moves, creating a trail of
volcanoes.
 The
Hawaiian Islands are an example of this
type of volcanic activity.